1. Field of the Invention
The present invention relates generally to a fluid compressor and more particularly to a fluid compressor for compressing a refrigerant in a refrigerating cycle.
2. Description of the Related Art
Conventionally, a fluid compressor for compressing, for example, a refrigerant gas in a refrigerating cycle has been developed. This fluid compressor, as compared to a reciprocal type compressor or a rotary type compressor etc., comprises a less number of parts and a simpler driving mechanism. In addition, in this fluid compressor, a check valve is dispensed with and the compression efficiency is enhanced.
In the compressor of this type, a rotary body or a piston is eccentrically situated within a cylinder having both end portions opened. Both end portions of the piston are journaled in a main bearing or a suction-side bearing, and a sub-bearing or a discharge-side bearing. The piston is eccentrical to the cylinder.
The main bearing and sub-bearing are inserted in both end portions of the cylinder, such that the bearings hermetically seal the openings at both end portions of the cylinder. A spiral groove is formed in the outer peripheral surface of the piston, and a blade is wound along the spiral groove so that the blade can freely project from and retreat in the groove.
The inside space in the cylinder is divided by the blade into a plurality of working chambers. The volumes of the working chambers are gradually decreased from the suction side of the cylinder towards the discharge side.
A motor unit is provided on the peripheral wall of the cylinder. When the motor unit is actuated and the cylinder is rotated, the cylinder and piston are rotated relative to each other and synchronously by means of a torque transmission mechanism interposed between the cylinder and piston.
Thereby, a low-pressure refrigerant gas is introduced into a sealed casing through a suction pipe connected to the sealed casing. The refrigerant gas is gradually compressed while it is conveyed from the working chamber at the suction-side end of the cylinder towards the chamber at the discharge-side end. When the refrigerant gas is discharged from the discharge-side end, it has a high pressure of a predetermined value. The high-pressure gas is supplied to a condenser through a discharge pipe connected to the cylinder. The condenser is situated outside the compressor and it is a component of the refrigerating cycle.
A modification of this compressor is disclosed, for example, in Published Unexamined Japanese Patent Application 2-19684 filed by the applicant of the present application.
In this compressor, a pair of spiral grooves are formed in the peripheral surface of the piston. These spiral grooves are formed symmetrical from an axially middle part of the piston towards both ends of the piston. Spiral blades are fitted in the respective spiral grooves.
A low-pressure refrigerant gas is sucked from, for example, an axially middle part of the cylinder. The gas is conveyed in two directions, i.e. towards both end portions of the cylinder, and compressed and then discharged from both end portions of the cylinder.
In the above-described compressor with on spiral groove in the piston, a lubricating oil is supplied to sliding parts of the compressor. The sliding parts include sliding surfaces defined by the side wall of the spiral groove and the side surface of the blade, sliding surfaces defined by the main bearing, cylinder and piston, and sliding surfaces defined by the sub-bearing, cylinder and piston.
Of course, the above-described compressor with a pair of spiral grooves and a pair of blades has sliding parts. Accordingly, oil supply means is required for supplying a lubricating oil to the sliding parts.
In this type of compressor, however, an optimal oil supply mechanism has not yet developed. Under the situation, oil supply means employed in the compressor with one spiral groove in the piston has been adopted in the compressor with two grooves and blades.
Because of this, while the sliding parts of one of the compression section (e.g. sliding surfaces between one spiral groove and the corresponding blade) is sufficiently supplied with oil, the sliding parts of the other compressing section is not. The resultant bad sealing property causes lowering of compression performance or increase of input.
The present invention was made in consideration of the above circumstances, and its object is to provide a fluid compressor having a pair of spiral grooves and a pair of blades, wherein the respective sliding parts are surely supplied with oil and smoothness of the sliding parts is ensured for long time.